. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. TEGUMENTS OF FISHES. 547 362. Cycloid scale, xxii. due to the presence of small round scales, about y^^tli in. diameter, with concentric and radiating lines: they are set deep in the derm. In the Sand-eel (^Aiitmodi/tes), the scales are proportionally larger, and one margin rises from the derm and pushes out- ward the portion of epiderra covering it: the dermal depression is limited to the oj^posite margin, and is deeper than in the Eel. The free part of the scale retains the reticular structure; in the imbedded part the
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. TEGUMENTS OF FISHES. 547 362. Cycloid scale, xxii. due to the presence of small round scales, about y^^tli in. diameter, with concentric and radiating lines: they are set deep in the derm. In the Sand-eel (^Aiitmodi/tes), the scales are proportionally larger, and one margin rises from the derm and pushes out- ward the portion of epiderra covering it: the dermal depression is limited to the oj^posite margin, and is deeper than in the Eel. The free part of the scale retains the reticular structure; in the imbedded part the areola; are obliterated in the direction from the centre to the circumference ; the radiating lines preserve their distance, but, being united by cross fibres close set, the structure appears to be laminated. The majority of flexible scales present the same pattern of concentric and radiating lines: the concentric lines are the finest, most numerous, and constant; they repeat the contour of the scale, and with most regularity at the anterior imbedded and covered part, where growth chiefly takes place, the stages of which are marked by these lines. The ' nucleus' or beginning of the scale is usually excentric, fig. .362, n. The ra- diating lines, fig. 362 and 363, r, r, are larger and fewer: they are most numerous in the Loach ( Cobltis), are sometimes confined to the forepart of the scale, fig. 363, or may be absent {Sulmo): they are furrows. The parts of the scale-margin between the ends of the radiating lines usually project in different degrees from a slight convexity, as in figs. 362, 363, to the form of pro- cesses. The latter are most common at the anterior implanted border of the scale (JEsox): in many fishes the opposite or free border has numerous tooth-like processes, and similar parts may project from the adjacent periphery of the scale in two or more rows. Such scales with a comb-like free border, fig. 363, t, characterise the fishes thence called ' ctenoid:' where
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